Real Madrid defender Sergio Ramos has warned Manchester United that they will have to contain a rampant Cristiano Ronaldo who is at the peak of his career in Wednesday's Champions League round of 16 tie at the Bernabeu.

Ronaldo, 27, scored a hat-trick in Real's 4-1 win over Sevilla on Saturday and will head into his first match against former club United in some of the best form of his career, according to Ramos.

The Spaniard was quick to point out the significance of suppressing United's attack in Madrid, insisting their will be no shortage of chances for his side to grab the upper hand.

"Cristiano is going through the best moment of his career and we are so lucky to have him at Real Madrid," Ramos said. "United is the most important game of our season. We shouldn't go crazy. We know it's going to be 180 minutes not just 90.

"It's true that over here it would be super-important to keep a clean sheet and try to maintain the offensive level we have. We have the players to create danger."

Saturday's win gave Real a much-needed confidence boost after a shock 1-0 loss to Granada last week threatened to derail the Spanish champions' hopes of European success.

An 83,000-strong home crowd showed Real's support hasn't dwindled despite their declining La Liga fortunes this season and Ramos believes Los Blancos are confident they can reach the Champions League quarter-finals.

"We reacted well after the loss against Granada," he said. "Madrid have to show their faces every day. It's true that this is the most important game of the season because we can't look to past years.

"We are going into this super-important match and mentally the group is convinced we will beat United."